In recent years, light emitting diodes (hereinafter also referred to as “LEDs”) are used as a light source for illumination from a view point of energy saving and downsizing. Light emitting devices using a combination of an LED and a light flux controlling member that controls the distribution of light emitted from the LED are used in place of fluorescent lamps and halogen lamps. In addition, direct surface light source devices incorporating the light emitting device are used as a backlight in image display devices of transmission type such as liquid crystal display apparatuses (for example, PTL 1).
The surface light source device disclosed in PTL 1 includes a substrate, a light emitting element (light emitting chip) disposed on the substrate, a light flux controlling member (lens) disposed on the substrate to cover the light emitting element and to control the distribution of the light emitted from the light emitting element, and a light diffusion member configured to allow the light emitted from the light flux controlling member to pass therethrough while diffusing the light. The light flux controlling member includes an incidence surface on which light emitted from the light emitting element is incident, an emission surface configured to emit, to the outside, the light incident on the incidence surface, and a rear surface formed on the side opposite to the emission surface. The light emitted from the light emitting element is incident on the light flux controlling member from the incidence surface. The light incident on the light flux controlling member reaches the emission surface and is emitted from the emission surface to the outside.